linux-kernel - [PATCH 3.16 322/370] net: alx: Work around the DMA RX overflow issue

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Message-ID: <lsq.1489146383.969358696@decadent.org.uk>
Date:   Fri, 10 Mar 2017 11:46:23 +0000
From:   Ben Hutchings <ben@...adent.org.uk>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:     akpm@...ux-foundation.org, "Eric Dumazet" <edumazet@...gle.com>,
        "Ole Lukoie" <olelukoie@...l.ru>, "Feng Tang" <feng.tang@...el.com>
Subject: [PATCH 3.16 322/370] net: alx: Work around the DMA RX overflow issue

3.16.42-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Feng Tang <feng.tang@...el.com>

[ Upstream commit 881d0327db37ad917a367c77aff1afa1ee41e0a9 ]

Note: This is a verified backported patch for stable 4.4 kernel, and it
could also be applied to 4.3/4.2/4.1/3.18/3.16

There is a problem with alx devices, that the network link will be
lost in 1-5 minutes after the device is up.

>>From debugging without datasheet, we found the error always
happen when the DMA RX address is set to 0x....fc0, which is very
likely to be a HW/silicon problem.

This patch will apply rx skb with 64 bytes longer space, and if the
allocated skb has a 0x...fc0 address, it will use skb_resever(skb, 64)
to advance the address, so that the RX overflow can be avoided.

Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=70761
Signed-off-by: Feng Tang <feng.tang@...el.com>
Suggested-by: Eric Dumazet <edumazet@...gle.com>
Tested-by: Ole Lukoie <olelukoie@...l.ru>
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 drivers/net/ethernet/atheros/alx/main.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

--- a/drivers/net/ethernet/atheros/alx/main.c
+++ b/drivers/net/ethernet/atheros/alx/main.c
@@ -86,9 +86,14 @@ static int alx_refill_rx_ring(struct alx
 	while (!cur_buf->skb && next != rxq->read_idx) {
 		struct alx_rfd *rfd = &rxq->rfd[cur];
 
-		skb = __netdev_alloc_skb(alx->dev, alx->rxbuf_size, gfp);
+		skb = __netdev_alloc_skb(alx->dev, alx->rxbuf_size + 64, gfp);
 		if (!skb)
 			break;
+
+		/* Workround for the HW RX DMA overflow issue */
+		if (((unsigned long)skb->data & 0xfff) == 0xfc0)
+			skb_reserve(skb, 64);
+
 		dma = dma_map_single(&alx->hw.pdev->dev,
 				     skb->data, alx->rxbuf_size,
 				     DMA_FROM_DEVICE);